The disclosure of Japanese Patent Application No. 2001-114399 filed on Apr. 12, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a high-pressure fuel supply system of an internal combustion engine.
2. Description of Related Art
In order to inject fuel directly into cylinders of the internal combustion engine, high-pressure fuel need be supplied to fuel injection valves corresponding to the respective cylinders. To this end, a high-pressure fuel supply system for supplying high-pressure fuel to the fuel injection valves is known in the art.
A generally known high-pressure fuel supply system includes a delivery pipe leading to each fuel injection valve, a high-pressure pump for feeding high-pressure fuel under pressure into the delivery pipe, and a low-pressure pump connected to the inlet side of the high-pressure pump in order to ensure entry or introduction of fuel into the high-pressure pump.
The high-pressure pump is an engine-driven pump that includes, e.g., a plunger that is slidably reciprocated within a cylinder by a cam moving in association with a crankshaft of the engine, a valve for opening and closing an inlet port of the cylinder, a spring for biasing the valve in a valve-opening direction (i.e., toward an open position), and a solenoid for closing the valve against the bias force of the spring.
When the plunger is under an intake stroke, the solenoid is held in a non-energized state, so that the valve is opened by the spring, and the fuel is introduced into the cylinder through the inlet port. When the plunger is under a discharge stroke, the solenoid is energized in response to a valve-closing signal applied thereto, so as to close the valve. Before the valve is closed, the fuel in the cylinder is returned to the low-pressure pump through the inlet port. After the valve is closed, the fuel in the cylinder is fed under pressure into the delivery pipe.
By controlling the timing of closing the valve in the discharge stroke, a suitably regulated amount of fuel can be fed under pressure into the delivery pipe. Thus, the amount of fuel fed to the delivery pipe can be controlled in accordance with the amount of fuel consumed at the delivery pipe, and the pressure in the delivery pipe can be maintained at around a desired high fuel pressure.
Upon a start of the engine, the fuel pressure in the delivery pipe is lowered to be approximately equal to the atmospheric pressure. Therefore, the fuel pressure in the delivery pipe need be raised quickly in order to achieve favorable fuel injection into the cylinders. It is therefore desirable to close the valve of the high-pressure pump at the same time that the discharge stroke starts, and feed the entire amount of fuel in the cylinder under pressure into the delivery pipe.
In the known fuel supply system, however, it is impossible to close the valve at the same time that the discharge stroke of the plunger starts for the following reason: in a starting period of the engine, it cannot be determined whether the high-pressure pump operating in synchronization with the crankshaft and a camshaft is in an intake stroke or a discharge stroke until a cylinder discrimination sensor identifies or discriminates individual cylinders from each other. (For example, the cylinder discrimination sensor is attached to the camshaft and generates a pulse each time the first cylinder reaches the top dead center of its intake stroke.) Accordingly, the valve is kept opened with the solenoid held in a non-energized state during a period from the start of cranking until the cylinders are discriminated from each other. With the valve thus kept opened, the high-pressure pump does not feed the fuel under pressure into the delivery pipe.
During the above period between the start of cranking and cylinder discrimination, the low-pressure pump, which is an electrically driven pump, is able to feed the fuel at the rated discharge pressure from the start of cranking. Thus, the discharge pressure of the low-pressure pump is applied to the delivery pipe through the high-pressure pump, whereby the delivery pipe can be raised to the rated discharge pressure of the low-pressure pump (e.g., 0.3 MPa). Nonetheless, this pressure is still much lower than the target high fuel pressure (e.g., 12 MPa) of the delivery pipe to be achieved in a normal operation of the engine, thus making it difficult to accomplish favorable fuel injection.
It is an object of the invention to provide a high-pressure fuel supply system of an internal combustion engine including an engine-driven high-pressure pump, which is capable of feeding a regulated amount of fuel under pressure from the high-pressure pump by controlling a duration of closing of a valve disposed at an inlet of the pump during a discharge stroke of the pump, and which is capable of feeding the fuel under pressure from the high-pressure pump in a starting period of the engine before cylinders are discriminated from each other, thereby to raise a fuel pressure in a high-pressure portion, such as a delivery pipe, to a sufficiently high level in a favorable manner.
To accomplish the above and/or other object(s), there is provided according to the invention a high-pressure fuel supply system of an internal combustion engine including a plurality of cylinders, which system includes a high-pressure pump driven by the internal combustion engine and operable with a cycle consisting of an intake stroke for receiving a fuel and a discharge stroke for delivering the fuel. The high-pressure pump includes a valve selectively placed in an open position to allow the fuel to be introduced into the high-pressure pump and in a closed position to allow the fuel to be fed under pressure to a high-pressure portion of the fuel supply system that is located downstream of the high-pressure pump. A controller of the fuel supply system generates commands for closing the valve to the high-pressure pump during starting of the engine before the cylinders are discriminated from each other, such that a period of the generated commands is shorter than a half of the cycle of operation of the high-pressure pump during starting of the engine, and, after starting of the engine, controls a duration of closing of the valve during the discharge stroke of the high-pressure pump so that a regulated amount of the fuel is fed under pressure to the high-pressure portion of the fuel supply system. With this arrangement, even before the cylinders are identified or discriminated from each other, the valve is closed during the discharge stroke of the high-pressure pump, and the fuel is fed under pressure from the high-pressure pump to the high-pressure portion of the system while the valve is being closed, whereby the fuel pressure in the high-pressure portion can be favorably raised to a sufficiently high level.